探討側下視丘引起失眠的相關神經以及其可能的控制迴路

Abstract

失眠為常見且嚴重影響健康的精神疾病，急性恐懼壓力事件常被認為可誘發急性覺醒維持，進一步演變為慢性失眠。過去多著重整體大腦網絡的過度覺醒現象。本研究聚焦於外側下視丘（lateral hypothalamus, LH）及其不同細胞亞群，結合TRAP2活動依賴性標記、化學遺傳學（DREADD）、基因工程細胞凋亡、光遺傳學與鈣離子影像技術，系統性探討恐懼壓力相關神經元對覺醒維持的功能角色。 本研究以小鼠為模型，首先利用TRAP2技術標記急性恐懼壓力下被活化的LH細胞，並於安全環境中僅以DREADD再活化，發現刺激這群細胞可誘發顯著且長時間的清醒狀態。此外，進一步以Caspase-3系統剔除LH內CRF神經元後，發現原恐懼壓力標定細胞失去長效覺醒能力，顯示CRF亞群對於持續覺醒維持反應具有必要性。對照實驗顯示，單獨活化LH-hypocretin神經元僅引發短暫覺醒，顯著弱於CRF神經元。進一步利用交叉標記與操控上游腦區，發現來自AHN（前下丘腦區）投射且於恐懼壓力下被動員的LH細胞，同樣可誘發長時間清醒，而vCA1（腹側海馬CA1）相關細胞則僅產生輕微影響。直接刺激AHN→LH-CRF神經迴路同樣可誘發長效覺醒。此外，鈣離子影像實驗則顯示AHN內GABA能神經元可作為調控恐懼壓力訊號傳遞至LH-CRF細胞的關鍵閘門。 綜合而言，本研究從細胞、迴路與行為層面建立恐懼壓力、LH-CRF神經元與覺醒維持之因果模型，證實LH-CRF神經元為恐懼壓力誘發長效覺醒的關鍵，並揭示上游腦區動態調控LH-CRF細胞活性的神經機制。這些發現有助於理解恐懼壓力相關長期失眠的神經生物學基礎，並為未來針對神經迴路的失眠精準治療提供新方向。

Insomnia is a common mental disorder with significant impacts on health. Acute fear-related stress events are often considered triggers for acute maintenance of wakefulness, which may further develop into chronic insomnia. Previous studies have mostly focused on global brain network hyperarousal phenomena. This study focused on the lateral hypothalamus (LH) and its different neuronal subpopulations, systematically investigating the functional roles of fear-related neurons in wakefulness maintenance by combining TRAP2 activity-dependent labeling, chemogenetics (DREADD), genetic cell ablation, and optogenetics. Using a mouse model, we first employed the TRAP2 system to label LH neurons recruited during acute fear stress, and then selectively reactivated these cells in a safe environment with DREADD. We found that stimulation of these cells induced significant and prolonged wakefulness. Furthermore, after ablation of CRF neurons in the LH using a Caspase-3 system, the original fear-stress-labeled cells lost their ability to induce long-lasting wakefulness, indicating that the CRF subpopulation is necessary for sustained arousal responses. Another experiment showed that activation of LH-orexinergic neurons alone only induced transient arousal, which was markedly weaker than that induced by CRF neurons. Through intersectional labeling and manipulation of upstream brain regions, we found that LH cells receiving inputs from the anterior hypothalamic nucleus (AHN) and recruited during fear stress could also induce prolonged wakefulness, whereas vCA1 (ventral hippocampal CA1)-related cells produced only minor effects. Direct stimulation of the AHN→LH-CRF neural circuit similarly induced long-lasting arousal. Calcium imaging experiment further showed that GABAergic neurons in the AHN serve as a key gate controlling the transmission of fear stress signals to LH-CRF cells. In summary, this study establishes a causal model linking fear stress, LH-CRF neurons, and maintenance of wakefulness at the cellular, circuit, and behavioral levels. We demonstrate that LH-CRF neurons are the key mediators of fear-induced prolonged wakefulness and reveal the neural mechanisms by which upstream regions dynamically regulate the activity of LH-CRF cells. These findings enhance our understanding of the neurobiological basis of long-term insomnia associated with fear-related stress and provide new directions for precise circuit-based interventions for insomnia.